# Winter's formula

**Winters' formula**,^{[1]} named for Dr. R.W. Winters,^{[2]} is a formula used to evaluate respiratory compensation when analyzing acid–base disorders and a metabolic acidosis is present.^{[3]}^{[4]} It can be given as

,

where HCO3^{−} is given in units of mEq/L and pCO_{2} will be in units of mmHg.

Winters' formula gives an expected value for the patient's P_{CO2}; the patient's actual (measured) P_{CO2}is then compared to this:

- If the two values correspond, respiratory compensation is considered to be adequate.
- If the measured P
_{CO2}is higher than the calculated value, there is also a primary respiratory acidosis. - If the measured P
_{CO2}is lower than the calculated value, there is also a primary respiratory alkalosis.

## Alkalosis

Note that Winter's formula pertains to settings of metabolic acidosis.

To calculate the expected pCO2 in the setting of metabolic alkalosis, the following equations are used:^{[5]}

- pCO2 = 0.7 [HCO3] + 20 mmHg +/- 5
- pCO2 = 0.7 [HCO3] + 21 mmHg

## References

- ↑ Albert MS, Dell RB, Winters RW (February 1967). "Quantitative displacement of acid-base equilibrium in metabolic acidosis".
*Annals of Internal Medicine*.**66**(2): 312–22. doi:10.7326/0003-4819-66-2-312. PMID 6016545. - ↑ Asch MJ, Dell RB, Williams GS, Cohen M, Winters RW (April 1969). "Time course for development of respiratory compensation in metabolic acidosis".
*The Journal of Laboratory and Clinical Medicine*.**73**(4): 610–5. PMID 5775132. - ↑ "Case 1: Acid Base Tutorial, University of Connecticut Health Center". Retrieved 2009-05-09.
- ↑ "Acid-Base Disorders: Acid-Base Regulation and Disorders".
*Merck Manual Professional*. Retrieved 2009-05-09. - ↑ Hasan, Ashfaq. "The Analysis of Blood Gases." Handbook of Blood Gas/Acid-Base Interpretation. Springer London, 2013. pp. 253-266.

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